1. Field of the Invention
The present invention relates to an exchange, more particularly to an asynchronous transfer mode (ATM) exchange which is comprised of a multistage cascade connection of ATM switches of self-routing module structures which are provided with n number of outgoing lines and N number of incoming lines and perform electrical processing for the exchange of ATM cells from the incoming lines and output the same to predetermined outgoing lines.
ATM switches of the above-mentioned self routing module (SRM) construction autonomously determine paths for ATM cells input from the incoming lines and output them to predetermined outgoing lines. Usually, such ATM switches are connected in a multistage cascade arrangement to form multistage self routing (MSSR) switches which in turn form the exchange. Exchanges comprised of such ATM switches are coming into use as they are able to perform exchange processing of large amounts of data such as video data at a high speed.
2. Description of the Related Art
The present invention relates primarily to the portion of the outgoing lines and incoming lines. In the past, ATM cells (data) exchanged at a high bit rate of, for example, 1.2 Gbps or 2.4 Gbps by a preceding ATM switch were passed through outgoing lines and incoming lines mainly comprised of coaxial cables and transferred to the next ATM switch.
There are, however, frequent demands for extension of exchanges to deal with insufficient line capacity. When extending exchanges, the practice is to increase the number of lines N in the N.times.N construction SRM's. For example, a 4.times.4 construction SRM is extended to an 8.times.8 construction SRM or to a 16.times.16 SRM or 64.times.64 SRM.
In this case, as will be explained later with reference to the figures (FIGS. 3, 4, and 5), if the scale of the switches is increased, the coaxial cables laid between each two adjacent stages become larger.
Connection of larger coaxial cables between ATM switches requires a certain amount of space to be secured between the different ATM switches and mounting of ATM switch boards on racks. If laying such a large amount of coaxial cables on the racks, however, the coaxial cables become as long as, for example, 100 meters.
Since high speed electrical signals of, for example, 1.2 Gbps are transferred on such coaxial cables, a length of 100 meters would mean a significant signal delay arising from stray capacities etc. and the danger of data error arising.
As a means of dealing with this, it may be considered to bundle in parallel 120 coaxial cables per highway, for example, and reduce the bit rate of the electrical signals transferred on the coaxial cables equally to 1/120 (10 Mbps). If this is done, however, the racks in the exchange would be buried in a tremendous number of coaxial cables, so this is really not practical.